ABSTRACT
Levels of energy expenditure are relevant to establishing positive or negative energy balance, corresponding to the development and regression of obesity. Skeletal muscle is the largest tissue of the body, commonly representing approximately 40% of total body weight. Energy metabolism in skeletal muscle accounts for roughly 20% of the basal metabolic rate and much larger proportions of whole-body energy expenditure during non-exercise activity thermogenesis (NEAT) states and during exercise. Futile cycles in skeletal muscle, such as sarcolipin-stimulated Ca-ATPase uncoupling and mitochondrial proton leak, can account for significant proportions of energy expenditure in this tissue. In the case of mitochondrial proton leak, this is approximately 50% of resting muscle energy expenditure, which thus corresponds to about 10% of the basal metabolic rate. There is significant interindividual variability in mass-specific metabolic rates and in activity of futile cycles that affect the propensity for obesity and its successful treatment. Increasing energy expenditure through increased ATP demand in muscle through NEAT, exercise, and futile cycles are approaches that can prevent and treat obesity.
